1. Field of the Invention
The present invention relates to a deposition process via laser ablation. More particularly, the present invention is suitable for forming electronic and microwave devices comprising oxide compounds.
2. Related Background Art
Laser ablation is one of the most suitable deposition process for producing excellent quality of thin films on substrate or workpiece. Laser ablation process has advantages, such as excellent stoichiometric stability of deposited film, when the process is used for depositing films of complex metal oxide compounds such as Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-x. There is another advantage in Laser ablation processing that it requires no electromagnetic fields which may possibly affect the charged particle contained in the deposited film. Therefore, laser ablation is expected to be employed as deposition process for the most promising nearterm devices.
Higaki et al (Institute of Electronics, Information and Communication Engineers, advanced conference paper, Apr. 26, 1991, hereinafter called "Reference 1") describes that a planar-type disk resonator formed when a thin layer of Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-x (referred to as "YBCO") is deposited by sputtering has excellent characteristics for the use in the microwave/millimeter-wave fields, such as temperature dependence of the surface resistance.
As described in the Reference 1, qualities of a thin film of oxides, such as crystallinity, are particularly important for microwave devices.
FIG. 9 shows an exploded perspective view of a resonator disclosed in the Reference 1. As shown in FIG. 9, a resonator 100 in accordance with Reference 1 has a configuration, in which a center dielectric layer 108 having a circular thin film 106 and rectangular thin films 107a and 107b thereon is sandwitched between an underlying lower dielectric layer 104 having a lower ground plane 102 of a gold thin film on its surface and an overlying upper dielectric layer 112 having an upper ground plane 110 of a gold thin film, by adhesion of these dielectric layers.
However, since the center dielectric layer is adhered to both the upper and the lower dielectric layer to form the device, high-frequency characteristics of the device may be affected with the adhesion conditions.
Holzapfel et.al. describes that c-axis oriented epitaxial thin films of YBa.sub.2 Cu.sub.3 O.sub.7-x had been formed on both the front and the back surfaces of a substrate having (100) plane of LaAlO.sub.3 and SrTiO.sub.3 by the laser ablation of off-axis arrangement [Holzapfel, B, et al., Applied Physics Letters, 61(26), pp. 3178-3180, 28 December 1992, hereinafter called "Reference 2"]. The disclosure of the Holzapfel et.al. is hereby incorporated by reference.
The Reference 2 suggests a possibility of forming thin films of oxides on both upper and lower surfaces of a dielectric substrate, thereby forming ground planes onto the dielectric substrate to produce resonator. However, Reference 2 does not describe any useful method for forming acceptable films for superior electronic or microwave devices on both the front and the back surfaces in one process.
Therefore, it is desirable to provide a method for forming more reliable member used for microwave devices by employing laser ablation.